1. Field of the Invention
This invention relates generally to novel fuel compositions for spark ignition internal combustion engines. More particularly, it relates to a novel additive combination for "nonleaded" gasoline compositions.
2. Description of the Prior Art
The incorporation of various organo-metallic compounds as antiknock agents in fuels for high compression, spark ignited, internal combustion engines has been practiced for some time. The most common organo-metallic compound used for this purpose is tetraethyl lead ("TEL"). Generally these organo-metallic compounds have served well as antiknock agents. However, certain environmental hazards are now associated with the alkyl lead components of these compounds. This circumstance has precipitated a series of Environmental Protection Agency ("EPA") mandates aimed at completely phasing out leaded gasolines.
Many alternatives to these organo-metallic compounds also have been proposed and/or used. For example organomanganese compounds such as cyclomatic manganese tricarbonyls particularly methylcyclopentadienyl manganese tricarbonyl ("MMT"), were once accepted alternatives to TEL. However, these compounds produced another set of environmental problems. Their use tends to steadily increase the amount of unoxidized and/or partially oxidized hydrocarbons emitted from engines commonly referred to as "engine out hydrocarbons" (EOHC). Fuels containing such organomanganese compounds gradually cause the emission of substantially higher levels of hydrocarbons than are permitted under law. Aggravating the air pollution problem, such organomanganese compounds, particularly MMT, when used at concentrations greater than about 1/16 per gram manganese per gallon, are believed to be responsible for catalytic converter plugging. Accordingly, under Federal Law the use of MMT is currently banned in all unleaded gasolines.
It is well known in the art that many lower molecular weight aliphatic alcohols possess antiknock properties. They have been used as motor fuels in their own right and they have also been used as antiknock additives in both leaded and nonleaded gasolines.
As might be expected, many attempts have been made to combine tetraethyl lead, cyclomatic manganese tricarbonyls, and/or lower aliphatic alcohols with petroleum hydrocarbon products boiling within the gasoline range. Some combinations are the result of chemical compounding, while others represent noncompounded physical blends in various combinations. Certain combinations of these ingredients have been blended with or without the use of stabilizers. U.S. Pat. No. 3,030,195 (the "195 patent") well summarizes the results of prior art efforts to physically blend TEL, MMT and certain lower aliphatic alcohol antiknock agents in gasoline without the aid of stabilizing agents. For example, the 195 patent points out that when lower aliphatic alcohols and TEL type compounds are present together in petroleum hydrocarbon gasolines, the antiknock effect achieved by the combination is substantially lower than would be expected in view of their known individual antiknock efficacies. This phenomena is commonly referred to as "negative lead susceptibilities". The 195 patent teaches that a positive synergism in the antiknock properties of leaded gasoline/alcohol fuel compositions can be obtained by adding a cyclomatic manganese tricarbonyl such as MMT to leaded gasoline compositions. However, at this time the technical advantages produced by such fuel compositions are being effectively negated by the phase out of lead containing antiknock additives.
Other investigations aimed at describing the physical properties of leaded gasoline/alcohol blends have shown that n-propanol and i-butanol give smaller octane increases than methanol or ethanol in leaded gasolines/alcohol blends. The antiknock qualities of nonleaded gasoline/alcohol blends have also been investigated. These investigations also indicate that alcohols in general are considerably more effective octane improvers in blends utilizing low octane gasoline components as compared to high octane gasolines. See, for example, Cox, Frank W., PHYSICAL PROPERTIES OF GASOLINE/ALCOHOL BLENDS, Bartlesville Energy Technology Center, Bartlesville, Okla. (1979).
It is also well known that lower molecular weight aliphatic alcohols and gasoline when blended together form nonideal mixtures with respect to octane numbers. This nonideal behavior results in an additional benefit in that the actual increase in octane value of a gasoline/alcohol mixture is greater than that expected from the amount of alcohol added and the octane value of the gasoline taken separately. Consequently, those skilled in this art generally use the octane value, known as "blending octane value" or the average of research and motor octane (R+M)/2, to estimate the effect of alcohol on the gasoline base. For example, depending upon the octane values of the base gasoline, methanol/gasoline blends have been reported to be 2 to 3 Motor Octane Number and as high as 16 Research Octane Number above the reported values for the base gasoline. In any event, such finished methanol/gasoline fuels normally are 1.5 to 3 octane points (R+M)/2 higher than the base fuel itself. See for example, Eccleston, B. H. and Cox, F. W., PHYSICAL PROPERTIES OF GASOLINE/METHANOL MIXTURES, Bartlesville Energy Research Center, Bartlesville, Okla. (1977).
Notwithstanding these antiknock benefits, methanol by itself is not widely used as a gasoline additive due to the number of serious technical and legal problems associated with its use. In the technical realm, the presence of even small amounts of water can cause serious operational problems. Methanol when used by itself (and to a lesser extent ethanol) tends to phase-separate from gasoline in the presence of water and/or when exposed to cold weather conditions. This tendency to phase-separate has been a major obstacle to the use of such alcohols as octane enhancers and gasoline extenders. Further, methanol, particularly when it has phase-separated from gasoline, is known to have harmful corrosive tendencies to certain fuel delivery and engine components.
For these and other reasons, Section 211(f)(a) of the Clean Air Act, as amended (42 USC 7445), governs the usage and introduction of additives in unleaded gasolines and specifically provides that no fuel or fuel additive may be first introduced into commerce that is not "substantially similar" to any fuel or fuel additive used in the certification of any 1974 or later model year vehicle. In July 1981, EPA defined "substantially similar" to include fuels with up to 2.0 wt. percent oxygen. Ethers or alcohols (except methanol) are acceptable additives if they otherwise meet these oxygen limitations. Methanol can be used as a de-icer when used up to 0.3 volume percent or be used for this purpose up to 2.75 volume percent when introduced with an equal volume of butanol or a higher molecular weight alcohol. However, the fuel must conform to the characteristics of an unleaded gasoline as specified by ASTM D 439. This definition of "substantially similar" provides a general rule for the inclusion of oxygenates in unleaded gasolines. Methyl tertiary butyl ether (MTBE) qualifies under the general 2% oxygen rule. This is equivalent to about 11% MTBE by volume, depending on the specific gravity of the gasoline.
The Clean Air Act under Section 211(f)(4) provides that the EPA Administrator may waive the prohibition on new fuels or fuel additives. However, prior to granting a waiver the Administrator must determine if the application meets the burden of demonstrating that the new fuel or fuel additive will not cause the failure of an emission control system or an emission standards(s). Under this section of the Act, the Administrator has both denied and granted several waiver requests.
The EPA has denied all previous waiver requests involving MMT in unleaded gasoline. The EPA denied Ethyl Corporation's MMT waiver applications because Ethyl failed to demonstrate that MMT at its proposed concentration levels of 1/16, 1/32 and 1/64 gram per gallon of gasoline would not cause or ultimately cause unacceptable hydrocarbon emissions. See generally Environmental Protection Agency in RE Applications for MMT Waiver, Federal Register, Vol. 43, No. 181, Monday, Sep. 18, 1978, and Ethyl Corp; Denial of Application for Fuel Waiver; Summary of Decision, Federal Register, Vol. 46, No. 230, Tuesday, Dec. 1, 1981.
The EPA has also denied several waiver requests for alcohol additives. However, on Sep. 23, 1981, Anafuel Unlimited was granted a waiver for a proprietary fuel called "Petrocoal" (see generally the Petrocoal Waiver and Supporting Docket EN 81-8). "Petrocoal" is a mixture of methanol and certain four-carbon alcohols in unleaded gasoline in the presence of a proprietary corrosion inhibitor. The fuel can contain up to 12 volume percent methanol and up to 15% total alcohols. The ratio of methanol to four-carbon alcohols cannot exceed 6.5 to 1. The fuel must meet ASTM D 439 specifications.
The EPA granted on Nov. 16, 1981 a request by ARCO for a waiver for mixtures of methanol and gasoline-grade tertiary butyl alcohol "GTBA" (see generally the Oxinal Waiver granted in the EPA and Supporting Docket EN-81-10). ARCO markets these mixtures under the name "Oxinol". The ratio of methanol to GTBA cannot exceed 1 to 1, and the concentration of oxygen in the finished fuel cannot exceed 3.5 weight percent. The 3.5% oxygen limit translates into about 9.6% by volume. The lower the methanol content, the greater the total alcohol volume allowable. At zero methanol content, the 3.5 weight percent oxygen is equivalent to about 16 volume percent GTBA.
In 1979, EPA granted a waiver for "gasohol", which contains 10 volume percent ethanol (see generally the Gasohol Waiver). However, the general rule of 2 weight percent oxygen would limit ethanol to about 5.5 volume percent. This left an "illegal" limit between the 5.5 and 10 percent levels. In 1982, EPA interpreted the "gasohol" waiver to include any amount up to 10 volume percent anhydrous ethanol in unleaded gasoline.
The above described legal limitations also follow from the physical properties of such alcohol gasoline compositions, e.g., vapor pressure, enleanment, and evaporative emissions which can be adversely affected by the presence of lower molecular weight alcohols such as methanol and ethanol.
For example, methanol is 50 percent by weight oxygen. This leads to a potential problem known in the art as "enleanment". Fuel introduction and delivery systems (e.g., fuel injection systems, carburetors) are designed and adjusted to provide a predetermined stoichiometric amount (ratio) of air to fuel, and hence the amount of oxygen to fuel. In fuel carburetors and in cars without oxygen sensing devices this predetermined stoichiometric ratio is calculated without regard for gasolines containing oxygen. If a gasoline contains excessive concentrations of oxygenated components such as methanol, the air (oxygen) to fuel ratio is significantly changed from the predetermined ratio. Significant deviations from the predetermined ratio causes poor ignition and combustion properties of the fuel. A high air (oxygen) to fuel ratio produced in this manner will cause the engine to run lean. If an engine's air (oxygen) to fuel ratio becomes too high or lean, the engine will fail to start and/or continue to run.
In effect, enleanment sets a technical limit on the total amount of any oxygenated component such as alcohol that can be incorporated into a gasoline without making major modifications to most fuel introduction and delivery systems. Moreover, higher air (oxygen) to fuel ratios also may contribute to the production of certain environmentally harmful nitrogen oxides.
An attribute of enleanment which heretofore has not been distinguished by those skilled in the art is called "technical enleanment". "Technical enleanment" is that unexpected phenomena which exhibits symptoms of enleanment occurring when the total air (oxygen) content of the finished fuel is not stoichiometrically or chemically lean. Such behavior is very similar to enleanment and includes engine stalling, lack of power, poor combustion, difficult start-ups (especially warm start-ups) and other problems normally associated with oxygen containing fuels, including alcohol/gasoline fuels and combustion/fuel systems which are known to be chemically or stoichiometrically lean. The difference between chemical or stoichiometric enleanment and "technical enleanment" is that traditional chemical or stoichiometric enleanment can be predicted from a chemical and/or stoichiometric basis, whereas "technical enleanment" is not predictable on the same basis.
Since the EPA has exclusive jurisdiction of unleaded gasoline additives, exhaust emissions are a major concern when incorporating alcohols into unleaded gasolines. Numerous studies on this subject, including prior EPA waiver applications for alcohol additives, exist in the literature. These studies generally show that carbon monoxide emissions are reduced, and that nitrogen oxide emissions are generally unchanged. Hydrocarbon emissions from such fuels generally vary. For example Appendix B of the EPA's Waiver for "Petrocoal" showed the fuel's hydrocarbon emissions to be unchanged, see Federal Register Vol. 46, No. 192, Monday, Oct. 5, 1981, Page 48978. However, in one of the more comprehensive studies on the subject prepared under the direction of the U.S. Energy Research and Development Administration, hydrocarbon emissions increased with the introduction of methanol. Hydrocarbon emissions increased further by increasing the methanol concentrations in the base gasoline. See J. R. Allsey, EXPERIMENTAL RESULTS USING METHANOL AND METHANOL/GASOLINE BLENDS AS AUTOMOTIVE ENGINE FUEL, Bartlesville Energy Research Center, Bartlesville, Okla. (1977).
Therefore, in view of the federally mandated ban on methyl cyclopentadienyl manganese tricarbonyls (MMT), the phase-out of leaded gasolines, and in further view of the above noted technical and legal problems associated with gasoline/alcohol blends, there now exists a very pressing need to find new families of environmentally safe antiknock agents and/or learn to use known antiknock agents in ways which are technically and environmentally acceptable. Applicants believe that the latter course holds the best immediate promise.